Utpal R. Vaidya

Effect of processing conditions on the dynamic mechanical properties of starch and anhydride functional polymer blends

Abstract Reactive blending of starch with ethylene-propylene-g-maleic anhydride (EPMA) and styrene maleic anhydride (SMA) copolymers was carried out in a batch mixer. The effect of processing conditions, such as mixer speed and mixing time, on the dynamic mechanical properties and morphology, was studied. Starch/EPMA blends showed two distinct glass transitions in the G′ and G″ plots, one corresponding to the starch and the other corresponding to EPMA. Starch/SMA blends exhibited one broad transition, since the glass transition temperatures of starch and SMA were in close proximity to one another. The starch in the blend was sensitive to the processing conditions used in this study. Increasing the mixing time from 10 to 20 min and increasing mixing speed from 50 to 100 rev min−1 resulted in increased melting of starch granules. Increasing the mixing speed and mixing time also resulted in increased degradation of starch, as evident from the gel permeation chromatography.

Properties of ternary blends of starch and maleated polymers of styrene and ethylene propylene rubber

Abstract The properties of starch/styrene maleic anhydride (SMA)/ethylene propylene maleic anhydride (EPMA) were studied at a constant starch composition of 60% by weight. The synthetic polymer content was 40% of total weight and contained 30, 20 and 10% SMA by weight, the rest being EPMA. Blends were made in a batch mixer as well as continuously in an extruder. The water absorption data showed that samples made by extrusion have less water resistance than samples made in a batch mixer. Dynamic mechanical analysis indicated three distinct glass transitions, corresponding to the glass transitions of EPMA, starch and SMA. Tests showed injection moulding gave higher tensile strength compared to compression moulding, and tensile strength increased with SMA content. Gel permeation chromatography data indicated there was degradation during mixing. Blending using an extruder caused more degradation of starch in the blends than when a batch mixer was used. Both scanning electron microscopy and optical microscopy showed that some starch was not melted during blending though the number and average size of unmelted starch granules decreased with decreasing SMA content. Scanning electron microscopy indicated the different morphologies of injection moulded samples at different locations in the mould.

Properties of injection moulded starch/synthetic polymer blends-I. Effect of processing parameters on physical properties

Corn starch was melt-blended in a twin screw extruder with ethylene vinyl acetate (EVAMA) and polyethylene (EMA) each having a maleic anhydride functional group that could interact with the hydroxyl groups in the starch. The percentage of starch in the blend was 70% by weight. These blends were injection moulded at different melt temperatures, screw speeds, injection pressures and back pressures. The effect of these processing parameters on the tensile strength, percentage elongation, break energy, flexural strength and flexural modulus are reported. Results from statistical analysis indicate that temperature and weldline affected some of the properties. Samples with weldline had lower tensile strength, break energy, and percentage elongation for starch/EVAMA blends. Similarly, samples with weldline had lower tensile strength and flexural modulus for starch/EMA blends. Starch/EVAMA blends absorbed between 22% and 37% by weight of water over a three month period, while starch/EMA blends absorbed between 20% and 27% over the same period. The diffusion mechanism varied from Fickian to anomalous, depending on the process conditions. For both blends, the process parameters had similar effects on the equilibrium water up-take and relaxation time. The major thermal degradation products were ethanoic acid and methanoic acid as identified by head-space-gas chromatography. Starch/EVAMA formed four times more ethanoic acid than the starch/EMA blend did during ageing, probably due to the cleavage of the acetate group in the vinyl acetate part of the EVAMA.

Properties of injection moulded starch/synthetic polymer blends—II. Evaluation of mechanical properties

The effect of the composition, starch type, inclusion of fibers, and the presence or absence of weldline on the mechanical properties of injection moulded starch and synthetic polymer blends were studied as a function of time. In addition, the effect on the mechanical properties after mixing a fraction of reground starch/EVAMA and starch/EMA materials generated from runners and sprues with the respective virgin blended material have been studied. We have also investigated the effects of annealing, and soaking in water on the tensile properties of these blend compositions. Scanning electron microscopy has been used to study the morphology of selected blends. Statistical analyses were done to delineate the significant effects of the above compositions on the tensile and flexural properties of the blends. A small amount of functionalized polymer has stabilized the phase morphology and led to enhanced properties. Corn starch yielded better tensile properties that wheat starch or wheat flour. Weldline (knitline) strength ranged from 55 to 95% of nonweldline values and was dependent on composition. Up to 25% of reground materials can be used without any detrimental effect on properties. Addition of fibers increased the tensile but not flexural strengths, though the weldline properties of samples containing fiber were poor. Fibers with medium aspect ratios (3-3.5) were found to give better properties. Soaking in water reduced the tensile properties significantly. The tensile properties for most compositions were invariant with time.